One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, that works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate a micro-actuator are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One type of micro-actuator, to which the instant invention is primarily directed, incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion or contraction thereof. The PZT micro-actuator is configured such that expansion or contraction of the PZT elements cause movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803, entitled “Micro-actuator and HGA” and JP 2002-074871, entitled “Head Gimbal Assembly Equipped with Actuator for Fine Position, Disk Drive Equipped with Head Gimbals Assembly, and Manufacture Method for Head Gimbal Assembly.”
FIG. 1a illustrates a head gimbal assembly 277 (HGA) of a conventional disk drive device incorporating a dual-stage actuator. The disk drive device includes, among other things, a magnetic disk and a drive arm 213 for driving the HGA 277 (HGA) with a slider 203 mounted thereon. The disk is mounted on a spindle motor which causes the disk to spin. A voice-coil motor (VCM) is provided for controlling the motion of the drive arm and, in turn, controlling the slider 203 to move from track to track across the surface of the disk, thereby enabling the read/write head to read data from or write data to the disk. In operation, a lift force is generated by the aerodynamic interaction between the slider, incorporating the read/write head, and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension 213 such that a predetermined flying height above the surface of the spinning disk is maintained over a full radial stroke of the drive arm 213.
However, because of the inherent tolerances of the VCM and the head suspension assembly, the slider 203 cannot achieve quick and fine position control which adversely impacts the ability of the read/write head to accurately read data from and write data to the disk. As a result, a PZT micro-actuator 205, as described above, is provided in order to improve the positional control of the slider and the read/write head. More particularly, the PZT micro-actuator 205 corrects the displacement of the slider 203 on a much smaller scale, as compared to the VCM, in order to compensate for the resonance tolerance of the VCM and head suspension assembly. The micro-actuator 205 enables, for example, the use of a smaller recording track pitch, and can increase the “tracks-per-inch” (TPI) value by 50% for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator 205 enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
As shown in FIG. 1a, one known type of micro-actuator is a U-shaped micro-actuator 205. This U-shaped micro-actuator 205 has two side arms that hold the slider therebetween and displace the slider by the movement of the side arms. However, movement of the side arms generates a reaction force in the mounting area that will be propagated to a suspension tongue and, in turn, to the suspension itself. The reaction force causes a suspension resonance, or vibration, that will negatively impact the dynamic performance of the HGA. The suspension resonance resulting from operation of the micro-actuator is one factor that limits the bandwidth of the disk drive device.
Referring to FIG. 1b, a conventional PZT micro-actuator 205 includes a ceramic U-shaped frame 297 which has two ceramic beams or side arms 207 each having a PZT element thereon. With reference to FIGS. 1a and 1b, the PZT micro-actuator 205 is physically coupled to a flexure 214. Three electrical connection balls 209 (gold ball bonding or solder ball bonding, GBB or SBB) are provided to couple the micro-actuator 205 to the suspension traces 210 located at the side of each of the ceramic beams 207. In addition, there are four metal balls 208 (GBB or SBB) for coupling the slider 203 to the traces 210.
FIG. 1c generally shows an exemplary process for assembling the slider 203 with the micro-actuator 205. As shown in FIG. 1c, the slider 203 is partially bonded with the two ceramic beams 207 at two predetermined positions 206 by epoxy 212. This bonding makes the movement of the slider 203 dependent on the movement of the ceramic beams 207 of the micro-actuator 205 in an easy and effective manner. A PZT element is attached on each of the ceramic beams 207 of the micro-actuator to enable controlled movement of the slider 203 through excitation of the PZT elements. More particularly, when power is supplied through the suspension traces 210, the PZT elements expand or contract to cause the two ceramic beams 207 of the U-shape frame 297 to deform, thereby making the slider 203 move on the track of the disk in order to fine tune the position of the read/write head. In this manner, controlled displacement of slider 203 can be achieved for fine positional tuning.
While the PZT micro-actuator described above provides an effective and reliable solution for fine tuning the position of the slider, it also results in certain disadvantages. More particularly, because the PZT micro-actuator 205 and the slider 203 are mounted on the suspension tongue, a suspension resonance is generated when the PZT micro-actuator 205 is excited. In other words, the translational motion of the micro-actuator used to displace the slider 203 causes a vibration in the suspension due to the constraint of the U-shaped frame 297 of the micro-actuator. This suspension vibration resonance corresponds to the resonance of the excited suspension base plate, thereby resulting in a significant vibration that limits the servo bandwidth and the capacity improvement of the disk drive device.
FIG. 2 shows a graph of the resonance gain verses frequency for both the excited base plate and excited PZT element on the micro-actuator. As shown in FIG. 2, the numeral 201 represents a resonance curve when the suspension base plate is excited and numeral 202 represents a resonance curve when the micro-actuator 205 is excited. The graph of FIG. 2 shows that under a frequency of 20 kHz, there are significant gain peaks for the suspension frequency response in both the positive and negative directions for both the base plate and the micro-actuator, which demonstrate an adverse resonance characteristic for the device. FIG. 2 also shows the correspondence between the base plate resonance and micro-actuator resonance which combine to magnify the resulting adverse vibration in the device.
Thus, there is a need for an improved micro-actuator for use in head gimbal assemblies and disk drive units that does not suffer from the above-mentioned vibration problems, yet still enables fine tuning of the read/write head.